As is widely known, automotive bodies include what are known as monocoque structures. Namely, automotive bodies are configured by body shells in which reinforcement framework members are joined to relevant portions such as portions on which stress acts, and portions that support heavy objects, in a box shaped structural body in which multiple molded panels are superimposed on each other and joined together.
FIG. 12A to FIG. 12D are explanatory diagrams respectively illustrating framework members 1 to 4, to be disposed at relevant portions of a body shell. As illustrated in FIG. 12A to FIG. 12D, the framework members 1 to 4 are generally manufactured as hat shaped members with hat shaped lateral cross-section profiles by pressing blanks, these being stock materials, using a punch and a die. More specifically, the framework members 1 to 4 are each configured including a top plate 5 (first wall), two ridge lines 6a, 6b formed along two edges of the top plate 5, two vertical walls 7a, 7b (second walls) respectively linked to the two ridge lines 6a, 6b, two bend lines 8a, 8b respectively linked to the two vertical walls 7a, 7b, and two flanges 9a, 9b (third walls) respectively linked to the two bend lines 8a, 8b. Note that FIG. 12D illustrates a case in which the framework member 4 has been spot welded to a closing plate P through the flanges 9a, 9b. 
As part of vehicle body weight reduction in order to both reduce CO2 emissions further, and also improve crash safety, there has been a recent trend toward making the framework members 1 to 4 even stronger and thinner. Accordingly, the framework members 1 to 4 are, for example, configured from sheet steel stock material with a tensile strength of 590 MPa or greater, 780 MPa or greater, and in some cases, 980 MPa or greater.
FIG. 13A to FIG. 13C are explanatory diagrams illustrating the occurrence of spring back (also referred to as “vertical wall warping” in the present specification) arising in the vertical walls 7a, 7b when demolding the framework members 1 to 4 after pressing. Specifically, FIG. 13A is a cross-section illustrating how the framework members 1 to 4 are pressed. FIG. 13B is a contour diagram illustrating moment distribution in the vertical walls 7a, 7b of the framework members 1 to 4 after pressing. FIG. 13C is a cross-section illustrating vertical wall warping in the framework members 1 to 4.
As illustrated in FIG. 13A, when pressing the framework members 1 to 4, portions B1, B2 of a blank B that are formed into the vertical walls 7a, 7b are subjected to bending, and bend-back, deformation by a punch 10 and a die 11 during the pressing process. Accordingly, as illustrated in FIG. 13B, accompanying the increased strength of the framework members 1 to 4, moments due to stress differences in the sheet thickness direction of the blank B (stress differences between stress at an outer side face (front face) and an inner side face (back face)) arise in the formed vertical walls 7a, 7b. More specifically, after forming, compressive stress acts on an outer side face (front face), and tensile stress acts on an inner side face (back face) at base end side portions of the vertical walls 7a, 7b. Accordingly, a moment (referred to below as “inward warp moment”) that would cause the base end side portions of the vertical walls 7a, 7b to warp so as to become convex on the front face side of the vertical walls 7a, 7b (curl around toward the inside of the framework members 1 to 4) arises in the base end side portions of the vertical walls 7a, 7b due to the difference between the stress in the outer side faces and the stress in the inner side faces of the vertical walls 7a, 7b. 
By contrast, after forming, tensile stress acts on the outer side face (front face), and compressive stress acts on the inner side face (back face) at leading end side portions of the vertical walls 7a, 7b. Accordingly, a moment (referred to below as “outward warp moment”) that would cause the leading end side portions of the vertical walls 7a, 7b to warp so as to become convex on the back face side of the vertical walls 7a, 7b (curl around toward the outside of the framework members 1 to 4) arises in the leading end side portions of the vertical walls 7a, 7b due to the difference between the stress in the outer side faces and the stress in the inner side faces of the vertical walls 7a, 7b. Moreover, as illustrated in FIG. 13C, when the pressure applied to the framework members 1 to 4 by the punch 10 and the die 11 is removed during demolding following pressing, vertical wall warping is liable to occur in which, due to elastic deformation recovery, the two vertical walls 7a, 7b depart from the shape they take on when applied with pressure (a manufactured article shape), and return to an opened-out shape (a shape in which the two flanges 9a, 9b have moved apart from each other).
As a countermeasure thereto, as illustrated in FIG. 14A to FIG. 14C, technology is known in which vertical wall warping is suppressed by providing beads 12, steps 13, or the like to parts of the vertical walls 7a, 7b. Moreover, for example, Japanese Patent No. 4984414 (Patent Document 1) describes technology in which vertical walls are formed with a continuous undulating shape in order to suppress spring back.
Moreover, Japanese Patent Application Laid-Open (JP-A) No. 2007-111725 (Patent Document 2) describes technology to reduce spring back in a pressed article that is pressed plural times. For example, as illustrated in FIG. 15, technology is described in which a pressed article that been pressed a first time (see the left side of FIG. 15) is pressed a second time using a punch with a larger width dimension (see the right side of FIG. 15) in order to reduce spring back in the pressed article.